In an inkjet print apparatus equipped with a serial-type inkjet printhead, the inkjet printhead is caused to scan in a primary scan direction and the printhead is driven in sync with the scanning thereof based upon a head drive signal obtained from image data to thereby discharge ink from the printhead nozzles and form an image on the printing medium, such as printing paper.
The inkjet head used in such an inkjet print apparatus will be described. Printing methods that are available for use with an inkjet printer include a method that utilizes electrothermal transducers (heaters), and another that utilizes piezoelectric elements, as discharge-energy generating elements that apply discharge energy for discharging ink droplets.
Both methods make it possible to discharge ink by applying electric signals to the discharge-energy generating elements. The former is advantageous in that little space is required for arraying the heaters constituted by the discharge-energy generating elements, the inkjet head is simple in structure and is capable of being made small in size, and a higher density can be achieved comparatively easily. A drawback, however, is that the heat produced by the heaters accumulates inside the head.
Accordingly, when printing is performed continuously at a high duty, the volume of the discharged ink droplets increases owing to a rise in the temperature of the head, refilling of the ink is not performed soon enough and discharge failure such as deviation from a normal direction or insufficient amount of ink occur.
A method that has been disclosed in order to solve this problem is to acquire printhead temperature information at a prescribed timing and lower the drive frequency of the printhead if the acquired temperature is greater than a predetermined temperature.
With the method described above, however, the amount of increase in printhead temperature subsequent to the prescribed timing cannot be estimated. For this reason, a value that attempts to take into account the maximum rise in temperature recorded after the prescribed timing is set as a threshold temperature. In this case, the threshold temperature is set low to an extent that takes the temperature rise into consideration. However, the actual rise in temperature depends upon printing duty subsequent to the prescribed timing. Consequently, even in a case where printing duty following the prescribed timing is low and a rise in temperature of the expected level does not occur, the drive frequency declines and, as a result, it is difficult to hold the decline in printing speed to the minimum.
Thus, in the prior art, it is difficult to minimize a decline in throughput while suppressing ink discharge failure due to a rise in temperature at the time of continuous printing.